A three-dimensional object manufacturing method including a 3D object forming step of forming a three-dimensional object by discharging a UV curing type ink, and thereafter, carrying out UV irradiation on the discharged ink to form a layer, and overlapping a plurality of layers is conventionally known (see e.g., Japanese Unexamined Patent Publication No. 2015-123687). For example, as shown in FIGS. 9A and 9B, the 3D object forming step is a step of forming the three-dimensional object by discharging a model material 91 serving as an ink to become at least a part of the three-dimensional object and a support material 92 serving as an ink at least disposed on a lower side of the model material 91 in a vertical direction indicated with an arrow 90a to support the model material 91, and thereafter, carrying out UV irradiation on the discharged model material 91 and the support material 92 to form a layer 93, and overlapping a plurality of layers 93. The 3D object forming step sometimes includes a step of moving a planarizing member 94 in an extending direction of the layer 93, that is, a direction indicated with an arrow 90b with respect to the model material 91 and the support material 92 while the model material 91 and the support material 92 are adjacent to each other to simultaneously planarize the surface of the model material 91 and the surface of the support material 92 with the planarizing member 94 before curing.